1. Field of the Invention
The present invention relates to transmitting a control channel shared by a plurality of users for uplink transmission in a communication system, and uplink transmission of packet data based on receipt of the control channel.
2. Description of Related Art
Expanded efforts are underway to support the evolution of the Universal Mobile Telecommunications System (UMTS) standard, which describes a network infrastructure implementing a next generation Wideband Code Division Multiple Access (W-CDMA) air interface technology. A UMTS typically includes a radio access network, referred to as a UMTS terrestrial radio access network (UTRAN). The UTRAN may interface with a variety of separate core networks (CN). The core networks in turn may communicate with other external networks (ISDN/PSDN, etc.) to pass information to and from a plurality of wireless users, or user equipments (UEs), that are served by radio network controllers (RNCs) and base transceiver stations (BTSs, also referred to as Node Bs), within the UTRAN, for example.
Standardizing bodies such as the 3rd Generation Partnership Project (3GPP and 3GPP2), a body which drafts technical specifications for the UMTS standard and other cellular technologies, have introduced several advanced technologies in an effort to ensure that any associated control information is carried in an efficient manner. Certain advanced or enabling technologies may include fast scheduling, Adaptive Modulation and Coding (AMC) and Hybrid Automatic Repeat Request (HARQ) technologies. These technologies have been introduced in an effort to improve overall system capacity. In general, a scheduler or scheduling function at a Node B (base station) selects a UE (mobile station) for transmission at a given time, and adaptive modulation and coding allows selection of the appropriate transport format (modulation and coding) for the current channel conditions seen by the UE.
AMC technologies enable a selection of a data rate and a transmission format (i.e., modulation level and channel coding rate) that best “suits” the scheduled user's prevailing channel conditions. Delays and measurement errors result in degraded performance from AMC.
HARQ allows combining of the original transmission with the new transmission, rather than to discard the original transmission. This may greatly improve the probability of correct decoding of the packet. The word “hybrid” in HARQ indicates that Forward Error Correction (FEC) techniques have been used in addition to ARQ techniques. Accordingly, HARQ helps to ensure that transmissions resulting in unsuccessful decoding, by themselves, are not wasted.
While much of the standardization to date has focused on the downlink (forward link from Node B/base station to UE/mobile station), similar enhancements are now being considered for the uplink (reverse link). Further evolution of 3G standards include enhanced uplink (EU) features to support high-speed reverse link packet access (uplink from mobile station to base station). Many of the techniques used in the forward link (i.e., fast scheduling, AMC, HARQ, etc.) may also be usable on the reverse link, so as to improve data rates and system capacity, for example.
In order to enable some of the above-mentioned technologies, control signaling is utilized on the uplink and downlink. The uplink signaling typically consists of ACK/NACK feedback for HARQ operation and channel quality indication (CQI), so that the UE can tell the Node B whether a previously transmission was received. The uplink signaling is carried over a physical channel known as a dedicated physical control channel (DPCCH). For downlink signaling, a shared control channel (SCCH) is used to carry scheduling and HARQ control information for a current transmission to the UE to process a corresponding data transmission, and/or to specify UE transmit rate for uplink transmissions of high speed data, for example. For supporting high speed data, the SCCH is known as a high speed shared control channel (HS-SCCH), as specified by the High Speed Downlink Packet Access specification (HSPDA) for UMTS.
One set of issues being addressed by 3GPP includes design considerations for control or signaling channels to conserve radio resources and to reduce the amount of interference or traffic in the uplink. Control or signaling information that is transmitted via a SCCH is typically encoded, e.g., with block codes or convolutional codes. As such, a UE must decode all the information in the SCCH in order to decode a signaling message that is then used for processing the corresponding data transmission from the Node B over a corresponding downlink shared channel (DSCH).
By way of example, signaling or control information in the SCCHs can include transmission format information such as code information (which codes are used for the data transmission), modulation information, Transport Block Size (TBS), and so on. The SCCHs are used on a shared basis among all the UEs such that each UE in a cell would read all the SCCHs transmitted in the downlink from a wireless network serving the UEs. Since a UE must decode and evaluate control data from a plurality of SCCHs received in the downlink, radio resources are being wasted, as the total number of bits the UE must process is a processing burden. The amount of data sent over these SCCHs thus taxes downlink bandwidth. Additionally, clogging in the uplink may occur as a UE transmits responses to control or signaling data it has decoded from several SCCHs.